The present invention relates to the field of electrophotographic reproduction and, more particularly, to dual layer organic photoconductive elements such as belts, drums, webs, or the like, which are used in machines such as copying machines. Reference is made to U.S. Pat. Nos. 3,615,415, 3,824,099 and 4,150,987 for their discussion of the general field of the present invention and for their disclosure of some of the specific materials and procedures over which the present invention represents an improvement.
Aforementioned U.S. Pat. Nos. 3,824,099 and 4,150,987 relate to dual layer organic photoconductive elements comprising a conductive substrate such as a paper, metallized plastic film or metal plate, supporting two basic layers, namely a charge generating layer and a charge transport layer. Either layer may be adjacent the conductive substrate, and an adhesive bonding layer may be applied to bond the charge generating layer to the electroconductive support.
During use, the photoconductive element is charged, exposed to light passed through or reflected by the light-transmissive areas of an imaged original sheet to conduct away the charge in the exposed areas, and the charge retaining or unexposed areas are either "inked" with toner which is transferred to a copy sheet or are first transferred to a copy sheet and then "inked" with toner thereon. The toner is fused on the copy sheet to form fixed images corresponding to the images present on the original sheet.
Dual layer organic photoconductive elements were developed in order to provide extremely fast response to light exposure within the visible range of the spectrum. Preferred materials in this respect are Chlorodiane Blue as the charge generating organic chemical of the charge generating layer and p-type hydrazones or triaryl pyrazolines as the organic chemicals of the charge transport layer.
Chlorodiane Blue is a preferred charge generating material because it has good stability and provides photoconductive elements having a desired shelf life or duration of storage prior to breakdown and deterioration or loss of the charge generating properties. Chlorodiane Blue also has a superior light sensitivity and charge generating properties over a broad portion of the visible light range, i.e., between 400 mu and 700 mu.
Charge generating layers based upon Chlorodiane Blue dye or other known charge generating organic chemicals are thin layers which contain the dye in solid particulate form and which therefore are relatively brittle and have low cohesive and adhesive strength.
In order to provide a bond between the charge generating layer and the conductive support, e.g., commonly a metallized plastic film such as aluminized polyester available from the duPont Company under the trademark Mylar, it is known from Example I of U.S. Pat. No. 4,150,987 to apply a bonding layer of synthetic thermoplastic resin such as a linear polyester resin having a glass transition temperature (Tg) larger than 60.degree. to the conductive support. U.S. Pat. No. 4,150,987 also discloses that the use of other known constituents may be included in the charge transport layer for enhanced adhesion.
We have discovered that known organic photoconductive elements, such as the elements described in the example given above, are still susceptible to delamination and having the problem of brittleness, especially after long term storage, whereby the bond between the charge generating layer and the electroconductive support becomes relatively easy to break down and the charge generating layer and charge transport layer also become relatively easy to peel or flake from the support to render the electroconductive element less desirable for its intended purpose.
Solutions to these types of problems are described in commonly assigned and copending U.S. patent application Ser. Nos. 214,362, filed Dec. 8, 1980, for "Photosensitive Elements and Process" by Chang et al, now abandoned, and 296,667, filed Aug. 26, 1981 for "Photosensitive Elements and Process" by Chang et al.